Entanglement at a Two-Dimensional Quantum Critical Point: a T=0 Projector Quantum Monte Carlo Study

TL;DR

This study uses large-scale quantum Monte Carlo simulations to analyze entanglement entropy at a 2+1D quantum critical point, revealing universal scaling behaviors and shape-dependent properties that suggest broader universality across different quantum critical systems.

Contribution

It provides the first detailed numerical analysis of the second Rènyi entropy at a 2+1D quantum critical point, identifying universal coefficients and shape-dependent scaling functions.

Findings

Universal vertex-induced logarithmic scaling coefficient identified.

Shape dependence of Rènyi entropy matches a known theoretical function.

Evidence suggests potential universality of the scaling function across QCPs.

Abstract

Although the leading-order scaling of entanglement entropy is non-universal at a quantum critical point (QCP), sub-leading scaling can contain universal behaviour. Such universal quantities are commonly studied in non-interacting field theories, however it typically requires numerical calculation to access them in interacting theories. In this paper, we use large-scale T=0 quantum Monte Carlo simulations to examine in detail the second R\'enyi entropy of entangled regions at the QCP in the transverse-field Ising model in 2+1 space-time dimensions -- a fixed point for which there is no exact result for the scaling of entanglement entropy. We calculate a universal coefficient of a vertex-induced logarithmic scaling for a polygonal entangled subregion, and compare the result to interacting and non-interacting theories. We also examine the shape-dependence of the R\'enyi entropy for finite-size toroidal lattices divided into two entangled cylinders by smooth boundaries. Remarkably, we find that the dependence on cylinder length follows a shape-dependent function calculated previously by Stephan {\it et al.} [New J. Phys., 15, 015004, (2013)] at the QCP corresponding to the 2+1 dimensional quantum Lifshitz free scalar field theory. The quality of the fit of our data to this scaling function, as well as the apparent cutoff-independent coefficient that results, presents tantalizing evidence that this function may reflect universal behaviour across these and other very disparate QCPs in 2+1 dimensional systems.